Sonic atomizing spray nozzle

ABSTRACT

A sonic atomizing spray nozzle (40) wherein a slurry (30) of finely-divided sulfur oxide absorbent particles in a carrier liquid is sprayed into a flue gas stream (12) entering a drying chamber (20) for effecting the removal of sulfur oxides therefrom as a dry salt. The slurry is sprayed through a continuous circumferential slit (70) as a radially outwardly directed thin sheet which traverses an axially-downwardly directed curtain of atomizing gas passing from an annular channel (66) circumscribing and bordering upon the continuous slit (70).

BACKGROUND OF THE INVENTION

The present invention relates in general to spray dryers, and moreparticularly, to a spray nozzle for atomizing and spraying a slurry offinely divided material into a spray drying chamber to be contacted witha hot drying gas therein.

Spray drying is well-known in the prior art and has been used for dryingsolutions or slurries of finely divided particulate material dissolvedor suspended in a volatile carrier liquid, most commonly water. Theslurry or solution to be processed is atomized and sprayed into a hotgas stream passing through the spray dryer. The volatile carrier liquidis evaporated, and the dissolved or suspended particulate material driedto a fine powder. Spray drying has for many years been used for dryingand processing food products, pharmaceuticals, and many other powderproducts.

More recently, spray drying has been found to be an effective method fortreating flue gases from fossil fuel-fired furnaces to remove gaseouspollutants, most commonly sulfur dioxide, therefrom. In such anapplication, a solution or slurry of sulfur oxide absorbent, such aslime, limestone, soda ash, or caustic soda, in water is atomized andsprayed into the spray drying chamber to contact hot flue gas from thefurnace. As the water in the slurry or solution is evaporated by heatfrom the hot flue gas, the sulfur oxide absorbent reactant containedtherein reacts with sulfur dioxides contained in the flue gas. Theresultant product is a dry powder of sulfur-containing salt.

A typical spray dryer generally comprises a housing defining a spraydrying chamber designed to provide the proper environment and residencetime for efficient drying of the solution or slurry. The drying gas istypically introduced to the vessel through an inlet at the top thereofand an outlet near the bottom thereof. The solution or slurry ofparticulate material to be dried is sprayed into the vessel in a finelydivided form through atomization means. The atomized solution or slurryis sprayed into the hot drying gas as it enters the spray drying chamberso as to intermix with the hot gas so that the volatile carrier liquidis evaporated and the dissolved or suspended particulate materialreduced to a fine, dry powder.

One type of atomization means being used in spray drying applications isa sonic atomizing spray nozzle. In such a device, sound waves aregenerated by impinging a high-velocity stream of a gas, most commonlyair, against a resonator, disposed at the outlet of the spray nozzle.Simultaneously, the liquid solution or slurry to be atomized is injectedinto the zone of sound waves generated by discharging the high-velocitygas against the resonator. The vibrations from the resonating soundwaves possess considerable energy and as a result, atomize the liquidinto very fine droplets.

It is extremely important in most all spray dryer applications, and inparticular in spray dryers applied to sulfur oxide scrubbing, that goodliquid atomization resulting in very fine droplet size be achieved.Often a sonic spray nozzle design proven in the laboratory fails toachieve this goal in field application as good atomization is frequentlylost during scale-up because the ratio of the atomizing gas flow area tothe area of the liquid flow area is not maintained constant at the valuefound in the laboratory to yield good atomization. Alternatively,scaled-up sonic spray nozzles wherein particular care is taken tomaintain a constant flow area ratio often suffer from loss of intimatecontact between the liquid and the atomizing gas and uneven slurrydistribution in the spray dryer.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a sonicatomizing spray nozzle which is adapted to be scaled-up to handleincreased slurry flow rates while maintaining good atomization byholding a constant atomizing gas flow area to liquid flow area ratio andsimultaneously ensuring even spray distribution and intimate contactbetween the liquid to be atomized and the atomizing gas.

Toward the fulfillment of this and other objectives which will beevident from the following description, the sonic atomizing spray nozzleof the present invention comprises a support body, an open-ended outercylindrical shell extending therefrom, an open-ended inner shelldisposed coaxially within the outer cylindrical shell, and a resonatorplate spaced from and facing the open end of the inner shell anddisposed coaxially therewith. An atomizing gas plenum is defined betweenthe inner and outer shells and a liquid plenum is defined within theinterior of the inner shell between the resonator plate and the innershell.

An annular channel is defined between the outer surface of the open endof the inner shell and the inner surface of the open end of the outershell which serves as a flow passage between the atomizing gas plenumand the open end of the outer shell through which atomizing gas ispassed axially to impinge the resonator plate and generate a series ofsound waves which atomize the liquid. A continuous circumferential slitis defined between the end face of the open end of the inner shell andthe surface of the resonator plate through which the slurry or solutionto be atomized passes radially outwardly into the zone of sound wavesestablished adjacent the open end of the outer cylindrical shell.

The annular channel through which the atomizing gas passes and thecircumferential slit through which the liquid passes are disposed atright angles to each other. The flow area of the annular channel isequal to the product of the outer perimeter of the inner shell and widthof the channel. The flow area of the circumferential slit is equal tothe product of the outer perimeter of the inner shell and the width ofthe slit. Accordingly, the ratio of gas flow area to liquid flow area isequal to the ratio of the width of the annular chamber to the width ofthe circumferential slit and is independent of the perimeter of theinner shell. As the flow area for slurry is directly proportional to theperimeter of the inner shell, the flow area can be increased in scalingfor higher slurry flow rates without changing the ratio of gas flow areato liquid flow rate. Therefore, the nozzle of the present invention iscapable of scale-up without disturbing atomization because the flow arearatio remains constant.

Furthermore, intimate contact between liquid and atomizing gas isensured because their respective injection ports both border the outerperimeter of the inner shell and are disposed at right angles to eachother. Uniform distribution of liquid spray is ensured by providing acircumferentially continuous slit through which liquid is injected intothe spray dryer from the liquid plenum of the nozzle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flow diagram illustrating a spray dryer apparatusembodying the spray nozzle of the present invention, the spray dryingapparatus being employed as an absorption chamber for removing sulfuroxides from hot flue gases as a dry sulfur-bearing salt.

FIG. 2 is a side elevational, cross-sectional view of the spray nozzleof the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

While the specification concludes with claims particularly pointing outand distinctly claiming a spray nozzle which may be utilized in anyspray dryer apparatus where a slurry or solution is to be contacted witha hot drying gas in order to dry the liquid carrier and reduce thedissolved slurried solids to a fine dry powder, it is believed that theinvention can be best described and better understood from the followingdescription of a preferred embodiment of the present invention inconjunction with a spray dryer apparatus being utilized as an absorptionchamber employed in removing sulfur oxides from hot flue gases generatedin a fossil fuel-fired furnace. It is to be understood, however, thatthe spray nozzle of the present invention can also be used in many otherspray drying applications well-known in the prior art. Referring now tothe drawing and to FIG. 1 in particular, therein is depicted a schematicflow diagram illustrating a spray drying apparatus employed as anabsorption chamber for removing sulfur oxides from hot flue gasgenerated in a fossil fuel-fired furnace. A sulfur-bearing fossil fuel,such as oil or coal, is combusted with air in furnace 10 to formcombustion products termed flue gas 12. The flue gas, including sulfuroxide gases generated during the combustion of the sulfur-bearing fuelwithin the furnace 10, exits from the furnace through convection bank14. The hot flue gas traversing convection bank 14 passes over variousheat exchange surfaces immersed therein in heat exchange relationshipwith a liquid such as water flowing through the heat exchange surface togenerate steam. The flue gas leaving convection bank 14 is thentypically passed through an air heater 16 to preheat the combustion airbeing supplied to the furnace 10. As the flue gas passes through airheater 16, being in indirect heat exchange relationship with thecombustion air being conveyed to the furnace, the flue gas is cooled toa temperature typically in the range of 100 to 200 C.

From the air heater, the flue gas 12 passes through duct 18 to one ormore spray dryer absorption chambers 20. Having traversed the spraydryer absorption chambers 20, the flue gas is drawn by induced draft fan22 through a dry particulate collector 24 and thence to a stack 26 forventing to the atmosphere.

As the hot flue gas 12 passes through the spray dryer absorption chamber20, it contacts an atomized spray 28 of sulfur oxide absorbent slurry 30supplied from slurry prep tank 32. The slurry 30 is prepared in slurryprep tank 32 by mixing a sulfur oxide absorbent such as lime, calciumhydroxide, soda ash, or caustic soda with a volatile carrier liquid,most commonly water. The sulfur oxide absorbent within the slurry reactswith the sulfur oxides contained in the flue gas as it passes throughspray dryer 20 forming sulfur-containing salts. At the same time, thewater in the slurry is evaporated by the sensible heat content of thehot flue gas whereby the sulfur-containing salts are reduced to a finepowder so that only dry particulates remain within the flue gas. Whilemuch of the dry particulate precipitates from the flue gas in the hopperof the spray dryer 20, the remainder of the dry particulate is removedfrom the flue gas as it passes through the dry particulate collector 24disposed downstream of the spray dryer 20. The dry sulfur-containingparticulate from the spray dryer 20 in the dry particulate collector 24is passed to collection tank 34 for subsequent disposal.

In order to obtain optimal sulfur oxide absorption efficiencies and tocompletely dry the resultant salts to a fine powder, it is extremelyimportant that the reactant slurry be brought into intimate contact withthe hot drying gas as a finely atomized, mist-like spray. In accordancewith Applicants' invention, there is provided a spray nozzlespecifically designed to provide intimate contact between the hot gasand a continuous circumferential thin sheet of slurry sprayed radiallyoutwardly through the atomizing gas into hot flue gas as it enters thedrying chamber.

Referring now to FIG. 2, there is depicted therein a spray nozzle 40having a support body 42 with an outer cylindrical shell 44 extendingdownwardly therefrom terminating with an open end 46 at its lowerextreme. The interior of the outer cylindrical shell 44 is divided intoan upper chamber 48 and a lower chamber 52 by an open-ended inner shell50 disposed coaxially within the outer shell 44 with its open end 54extending through the open end 46 of the outer cylindrical shell 44. Aresonator plate 56 having a recessed rim 58 about its outercircumference is spaced from and facing the open end 54 of the innershell 50 and is disposed substantially coaxially therewith. A stem 60extends coaxially through the inner and outer shells to link theresonator plate 56 to the support body 42 for supporting the resonatorplate 56 therefrom.

The upper chamber 48 forms an atomizing gas plenum and is connected influid communication with a supply of atomizing gas, most commonlycompressed air, through atomizing gas feed inlet 62 which opens into theplenum 48. The lower chamber 52 forms a liquid, i.e., slurry orsolution, plenum chamber which is connected in fluid communication withprep tank 32 through liquid feed means 64. In the preferred embodiment,the stem 60 connecting the resonator plate 56 to the support body 42comprises a tubular shell, the interior 63 of which provides a flow paththrough which slurry is fed to the lower chamber 52. A plurality ofopenings 64 in the wall of the tubular stem 60 provide fluidcommunication between the interior of the stem 60 and the liquid plenum52.

An annular channel 66 is formed between the outer surface of the openend 54 of the inner shell 50 and the inner surface of the open end 46 ofthe outer cylindrical shell 44. The annular channel 66 provides a flowpassage for atomizing gas to pass from the atomizing gas plenum 48 outof the open end 46 of the outer shell 44 to impinge against the recessedrim 58 of the resonator plate 56 to generate sound waves. The flow areaof the annular opening 68 at the end of the annular channel 66 is equalto the product of the outer perimeter 72 of the inner shell 50 and thewidth of the channel 66.

A continuous circumferential slit 70 is formed between the resonatorplate 56 and the end face of the open end 54 of the inner shell 50. Thecontinuous circumferential slit 70 provides a liquid passage for flowcommunication between the liquid plenum 52 and the zone of sound wavesexisting adjacent the open end 46 of the outer cylindrical shell 44. Thecontinuous circumferential slit 70 provides for a sheet of liquid beingsprayed into the spray dryer thereby ensuring that uniform distributionof liquid spray is achieved.

As seen in FIG. 2, the continuous circumferential slit 70 and theopening 68 to the annular channel 66 are disposed at right angles toeach other and share a common boundary: the outer perimeter 72 of theopen end 54 of the inner shell 50. Intimate contact is ensured betweenliquid and atomizing gas as the liquid is injected radially outwardlythrough slit 70 and must traverse the atomizing gas passing axiallydownward through opening 68 at the end of the annular channel 66.

The flow area of the continuous slit 70 is equal to the product of theouter perimeter 72 of the inner shell 50 and the width of the slit 70.As the continuous slit 70 and the annular opening 68 share the perimeter72 of the inner shell 50 as a common boundary, the ratio of atomizinggas flow area to liquid flow area is equivalent to the ratio of thewidth of the annular opening 68 to the width of the continuous slit 70.

Therefore, in the nozzle of the present invention, the ratio of the gasflow area to liquid flow area is independent of the outer perimeterdimension of the inner shell 50 even though both flow areas are directlydependent thereupon. Accordingly, a nozzle can be scaled-up to handlehigher liquid flow rates, and therefore higher atomizing gas rates,simply by increasing the perimeter of the inner shell in a linearfashion. Both the gas flow area and liquid flow area would increase indirect proportion to the increase in perimeter while the ratio of thegas flow area to the liquid flow area, and therefore the atomizationcharacteristics of the nozzle, would remain the same.

In the preferred embodiment of the invention shown in FIG. 2, the innershell 50 comprises an open-ended conical annular shell 74 extendingoutwardly from the stem 60 toward the outer shell 44 at its open end. Acylindrical rim 76 extends axially downward from the conical shell 74 inclosely-spaced relationship to the open end 46 of the outer cylindricalshell 44. The annular channel 66 is defined by the circumferential spacebetween the outer surface of the cylindrical rim 76 and the innersurface of the outer cylindrical shell 44. The continuous slit 70 isdefined by the gap between the end face of the cylindrical rim 76 andthe resonator plate 56. The outer radial edge of the cylindrical rim 76serves as a common boundary for the continuous slit 70 and the annularopening 68.

An additional aspect of the present invention which warrants particularmention is the provision of a streamline surface as provided by theouter surface of the cylindrical shell 44. In most prior art nozzles,the outer surface of the nozzle body turns inward toward the center ofthe nozzle at the lower end of the nozzle. This inwardly projectingsurface provides an area adjacent the slurry injection ports forparticles in the slurry to strike and stick to resulting in a depositforming thereon which can adversely effect nozzle performance. Theprovision of a cylindrical outer shell precludes any buildup of depositsof the outer surface of the nozzle as no portion of the outer surface ofthe outer cylindrical shell 44 is exposed to slurry contact.

While a preferred embodiment of the present invention has been shown anddescribed for purposes of illustration and complying with the best moderequirements of 35 USC 112, it is evident that certain aspects of theinvention are not limited to the particular details illustrated in thedrawing and discussed in the specification. Therefore, the inventiondescribed herein is not to be construed as limited to the specificembodiment of a spray dryer apparatus for sulfur oxide removal asdescribed herein, but is intended to encompass all variations andapplications that do not depart from the spirit and scope of theinvention as described in the appended claims.

We claim:
 1. A spray nozzle comprising:a. a support body; b. anopen-ended outer cylindrical shell extending from said support body; c.a support stem extending from said support body coaxially through saidouter cylindrical shell and open end thereof; d. an open-ended innershell disposed coaxially within and in spaced relationship from saidouter shell so as to define a first plenum chamber between said innershell and said outer shell and a second plenum chamber within theinterior of said inner shell, the open end of said inner shell extendingto the open end of said outer shell in closely spaced relationshiptherewith thereby defining a circumferentially continuous annularchannel between the outer wall of said inner shell and the inner wall ofsaid outer shell, said annular channel providing a gas passage for flowcommunication between said first plenum chamber and the open end of saidouter shell, and providing an annular discharge outlet; e. a resonatorplate supported from said stem in spaced relationship from and facingthe open end of said inner shell and disposed substantially coaxiallytherewith thereby defining a continuous circumferential slit betweensaid resonator plate and the open end of said inner shell about theouter edge thereof, said continuous circumferential slit providing aliquid passage for flow communication between the second plenum chamberand the open end of said outer shell, said circumferential slit and saidannular channel disposed at substantially right angles along the outeredge of said inner shell, said annular discharge outlet discharging onsaid resonator plate; f. atomizing gas-feeding means communicating withsaid first plenum chamber; and g. liquid-feeding means communicatingwith said second plenum chamber.
 2. A spray nozzle as recited in claim 1wherein said stem comprises a tubular shell having a plurality of holesin its wall opening into said liquid plenum chamber, said stemcommunicating with said liquid feeding means and providing a flowpassage to said liquid plenum chamber.
 3. A spray nozzle comprising:a. asupport body; b. An open-end cylindrical outer shell extending from saidsupport body; c. A support stem extending from said support bodycoaxially through said cylindrical outer shell and the open end thereof;d. an open-end conical inner shell disposed coaxially within saidcylindrical outer shell and extending outwardly from said stem towardsaid cylindrical outer shell thereby defining a first plenum chamberbetween said conical inner shell and said cylindrical outer shell and asecond plenum chamber within the interior of said conical inner shell,said conical inner shell having a cylindrical rim extending axiallytherefrom at its open end in closely-spaced relationship to saidcylindrical outer shell to the open end of said cylindrical outer shellthereby defining a circumferentially continuous annular channel betweenthe outer surface of the cylindrical rim and the inner surface of saidcylindrical outer shell, said circumferentially continuous annularchannel extending between said first plenum chamber and the open end ofsaid cylindrical outer shell, and providing an annular discharge outlet;e. a resonator plate supported from said stem in spaced relationshipfrom and facing the open end of said inner shell and disposedsubstantially coaxially therewith thereby defining a continuouscircumferntial slit between said resonator plate and the open end ofsaid conical inner shell about the outer edge of the cylindrical rimextending from said inner shell providing a flow passage between saidsecond plenum chamber and the open end of said outer shell, saidcontinuous circumferential slit and said annular channel disposed atright angles to each other along the outer circumferential edge of thecylindrical rim extending from said conical inner shell, said annulardischarge outlet discharging on said resonator plate; f. atomizinggas-feeding means communicating with said first plenum chamber; and g.liquid-feeding means communicating with said second plenum chamber.
 4. Aspray nozzle as recited in claim 3 wherein said support stem comprises atubular shell communicating with said liquid-feeding means and having aplurality of holes in its wall opening into said second plenum chamberthereby providing flow passageway from said liquid-feeding means to saidsecond plenum chamber.